Many of us have been to a race track or watched NASCAR (National Association of Stock Car Auto Racing) races on television. Some of us are enthralled by these sleek, high-speed cars hurtling along at velocities where any mistake could be lethal. Yet deaths in this sport are relatively rare due to the fact that officials are implementing new technologies daily to make cars and racetracks even safer. Surprisingly, physics is the key to this safety. Understanding the powerful forces that operate during a race allows scientists and engineers to create protective technologies.

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One of the forces NASCAR has to work around is called a "g-force." This is the same force a pilot feels when doing loops or turns in their plane. This force is explained by Newton’s first and second laws. Newton's first law states that an object at rest tends to stay at rest and an object in motion tends to stay in motion with the same direction and speed, unless acted upon by an outside force. Newton's second law states that when there is an unbalanced force, the object will accelerate in the direction of that unbalanced force at a rate that is directly proportional to the unbalanced force and inversely proportional to the object's mass. Therefore, you would be subjected to g-forces in your own car when you speed up quickly and your inertia, or resistance to a change in your state of motion, keeps you pinned against your seat as it accelerates forward; or if your car were to stop suddenly your inertia wants you to keep moving forward and you are restrained by your seatbelt as you are thrown forward towards your dashboard. When your car speeds up or changes direction, your body wants to remain moving in its original direction at its original speed. This is called inertia. The fictitious force that seems to be pushing you in the opposite direction is called a g-force. G-forces are measured relative to the Earth’s acceleration due to gravity: 9.8 m/sec2 or 32 ft/sec2. For example, someone experiencing 2 g’s of acceleration would feel as though a force equal to twice the product of their mass times gravity was pushing against them. When drivers accelerate or turn corners, they experience a push in the direction opposite to the one they are accelerating. At 5 g’s it is possible for a driver to lose consciousness or become dizzy. During a crash, the car and driver may be subjected to forces of over 100 g’s.

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Another force that is important in racing is down force. As air passes over the car at high rates of speed, the aerodynamics of the car cause the air to push the car down closer to the ground. This down force gives the car more traction and allows it to maintain its high speed throughout turns. This effect is the exact opposite of what happens with plane wings, which are designed to create lift. When a car is involved in a wreck, though, it sometimes loses its down force and can act more like a wing. This is what causes a car to flip and hurtle through the air, picking up height and speed, making the final impact even more dangerous for the drivers and spectators.

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Using physics, engineers have come up with a partial solution to this problem. When a stock car is in a wreck and starts to spin, losing much of its down force, flaps on the top of the car are sucked open. These roof flaps disrupt air flow over the top of the car and typically the car will spin only once. Even if this is not the case, and the car spins numerous times, the roof flaps keep the car close to the ground as it spins. Keeping a car on the ground while it is spinning is important because the friction between the tires and the racetrack reduces the speed of the car. By slowing the car down, the roof flaps either let the driver regain control of the car or decrease the force of the impact the car makes with any objects in its path.

As dangerous as the sport of race car driving may be, there are many more devices that protect the driver from these dangerous forces. First the very design of the car is shielding. The driver is surrounded by a steel roll cage that prevents him from being squished. (see picture below) The car’s fuel cell is specially designed too. It has four braces to keep it attached to the car. In addition, it is filled with foam so that if it does ignite the foam will absorb the energy of the explosion. Finally, the engine has check valves that will cut off the flow of fuel to the engine if it is separated from the car.

Even the tires are designed for safety. They are double lined so that if the outer tire explodes the inner tire remains intact and the driver can drive to safety. Plus, air is removed from the tire and replaced with nitrogen. When the tires become super heated the moisture in the air vaporizes and expands making a noticeable difference in the cars handling. Nitrogen is less likely to expand the air and gives the driver more control of the car.

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Recently, two technologies have become more and more common. They include the soft wall and Head and Neck Support (Hans) due largely to the four deaths of NASCAR drivers-- Adam Petty, Kenny Irwin, Tony Roper and Dale Earnhardt Sr. All of them died during the 2000-2001 year when their cars slammed into concrete retaining walls. On impact their heads snapped forward causing a fracture at the base of their skulls. To counteract this a few drivers are now trying out the Head and Neck support system, design by Dr. Robert Hubbard, and his brother-in-law, Jim Downing. This 1.5 pound device is composed of two flexible tethers that latch the helmet to the seat, preventing severe whip lash.

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The soft wall is another protective measure. When a car hits a soft wall it collapses inward absorbing the impact and cushioning the driver from the force of the crash. Many NASCAR track are beginning to implement this technology and the Daytona International Speedway, for example, is one of seven tracks that now have soft walls. They recently constructed a Steel and Foam EnergyReduction Barrier, which was completed just in time for the 2004 Pepsi 400. These soft walls cover the dangerous turns of the track where most crashes occur at speeds in excess of 200 miles per hour. This new measure is likely to save several lives in the years to come. With all of these safety measure physics has surely conquered the forces of the race track.

According to the article, race car tires are filled with nitrogen rather than air. This improves safety for the driver because

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A. air contains moisture that causes hot tires to expand and over inflateB. nitrogen is less flammable than airC. tires that are not double lined explode more frequentlyD. air can liquify at extremely high temperatures

A race car flips and starts to go airborne. The driver is confident that his car will come through for him. Which safety feature is he counting on to counteract the lift?

G-forces are explained by Newton’s first and second laws. Which of the following is NOT a foundation of that law?

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A. objects at rest tend to stay at restB. objects are not affected by outside forcesC. objects in motion tend to stay in motion at the same direction and speedD. an object's velocity changes when acted upon by an outside force

Which of the following states the main idea of the story?

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A. down force is important to racingB. car design increases safetyC. physics is the key to safety in race car drivingD. one of the forces NASCAR has to work around is called g force

A. air passes over the car at high rates of speedB. the aerodynamics of the car cause the air to push the car down close to the groundC. it causes the car to flip and hurtle through the airD. down force gives the car more traction

Which of the following supports the fact that “the very design of the car is shielding”?

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A. The HANS device stops a driver’s head from snapping forward on impact.B. The driver is surrounded by a steel roll cage that prevents him from being crushed.C. The soft wall collapses inward, absorbing the impact.D. When drivers accelerate or turn corners, they experience a push in the direction opposite to the one in which they are accelerating.

Which of the following is NOT a device used for the safety of the stock car and its driver in a NASCAR race?